Preparing your tracks for professional mastering...

[safeandsound]

Hi again, my personal preference which will be fine for any mastering engineer also........

Operate your DAW at 24 bit
Export your mix at 24 bit stereo interleaved
Sample rate as is (in your mix session in your DAW, no need to convert it)
No limiter on master output
Check for clipping (exceeding digital zero) on master output

If you zoom in on a peak in the exported files waveform your peak should not be squared off or flat topped.
This suggests that you have clipped the master stereo output bus. Before exporting you can also just
look to ensure the peak light does not come on on the master output.

0dBFS means the numbers in the digital system have run out and beyond this the signal is no longer accurately represented.
The numbers representing the signal level (voltage) of any given sample are finite. At 0dBFS it is like a switch....

< 0dBFS = accurate representation
> 0dBFS = no longer represents signal accurately.

cheers

Barry